Toning photographic images



Patented Feb. 10, 1942 TONING rnorocaarmc moss Alan M. Gnndelfinger and Ityne S. Trimble, Los

Angeles, Calii., assignors to Cinecolor, Incorporated, Los Angeles, Call! a corporation of California No Drawing. Application December 20, 1938,

Serial N0. 246,848

s Claims. (Cl. 95-88) Our invention relates generally to color photography, and has particular reference to the production of metallic-toned images that are both fine-grained and well-defined in appearance. In many instances and particularly where sound track images are to be colored, it is quite essential that the images be as sharply defined v as possible, but it has been found that the conditions which make for good definition in toned images produce an image which is distinctly grainy in appearance,

In motion picture work, where the images are to be greatly magnified by projection on a screen, graininess is very undesirable, since it materially detracts from the pleasing 'appearance of the picture. Furthermore, excessive graininess in sound track images reduces the quality of their sound reproduction.

This problem of graininess vs. definition is always present when it is desired to tone the sound track images and one or more component picture images simultaneously with the same solution. For example, for many reasons it is often desirable to use an iron tone to color both the blue component'images in a picture and their accompanying sound track in one step, and we have found that when the toning solution is toning solution is adjusted to 'give excellent definition and consequently good sound reproduction.

the images will exhibit such apparent graininess as to be unsatisfactory.

35 tains a silver salt when first formed. In solutions, such as the one above containing a halide,

It is, therefore, the major object of our invention to overcome these obstacles and to provide a process of toning photographic images whereby the images are diffusely colored throughout their image area, and are thus satisfactory for picture projection, which said images also have unusually good definition, and are, therefore, capable of giving optimum reproduction quality.

In general, we accomplish our object by first treating the silver image with a toning solution which has been adjusted to give a diifused image, that is to say, the tone is of suchcharacter that a certain amount of bleeding or diffusion of the color throughout the gelatin in the immediate vicinity of the salt grains forming the image will be had. This bleeding or diffusion of the color within the image area colorsthe image to present a more or less uniform colored appearance. However, in using such a tone, the color also bleeds outwardly from the image, and thus creates a halo or fringe of diffused color entirely surrounding the image proper.

In the specification and claims, the term "image will be used to denote the original image area defined by free silver in the first instance, and metallic salt grains subsequently, and the term "fringe will be used to denote the diffused outline surrounding the image proper, it being understood that the term diffused image wherever used herein means an image formed of colored grains, whose color has bled into the surrounding emulsion between and among the grains to give a more or less uniformly colored image without apparent graininess.

In the preferred form of our invention, a photographic silver image is first produced by exposure and development of a light sensitive silver salt in conventional manner, and is then toned with a suitable metallic tone, for example an iron'toning solution, such as the following:

Ferric ammonium oxalate Grams 6 Potassium ferricyanide do-- 6 Ammonium chloride do 10 Hydrochloric acid (cone) cc-- 5 Water to make Liter 1 This treatment converts the silver image to a Prussian Blue image which is generally considered to be ferric ferrocyanide and/or a double salt of ferric ferrocyanide and an alkali metal ferrocyanide, and in either case, the image conthe silver salt in the resulting Prussian Blue image will be a silver halide, but if a toning solution is used which does notcontain a halide, the silver is in the form of silver ferrocyanide.

As previously mentioned, it is possible to control the amount of diffusion and thereby the amount of fringing in the toned image by controlling the amount of available iron in the toning solution, and we have found that the degree of diffusion varies directly as the ratio of the ferricyanide ion concentration to the ferric ion concentration in the toning solution. The exact proportions of the various constituents of the toning solution and the precise ratio between ferricyanide and ferric ion concentrations may be varied between comparatively wide limgelatin between the salt grains and causes the Effpen ing pon the type of emulsion used,

the density of the images, the type of image desired, and the other steps of the general color process. It is to be borne in mind, however, that the. toning solution must be adjusted so as to give images which are sumciently diffused to be satisfactory for picture projection, which means of course that a definite fringe will be produced.

After the image has been toned, the film is preferably washed and is then treated with a solution capable of eliminating the fringe, this treatment being continued until the fringe is substantially eliminated, care being taken, however, to stop the treatment before the color or the structure of the image is materially modified. This elimination of the fringe gives us once again an image with definition suitable for all purposes, and one still with little apparent graininess. For this purpose, we prefer to use a solution which will reduce the iron in Prussian Blue from the ferric state to the ferrous state, a suitable reducing agent of this nature being an alkali metal sulphite, such as sodium sulphite.

When treating a Prussian Blue image, such as the one obtained by using a toning solution of the nature above described, we have found that a concentration of about 1.4%, i. e. approximately 14 grams of sodium sulphite to a liter of water, will in approximately 3 minutes substantially eliminate the color in the fringe without materially affecting the color or structure of the image. The film is then thoroughly washed, and is thereupon ready for such further treatment as may be desired in order to complete the color process.

While we do not wish to be limited to the following theory, it is our belief that there are several reactions going on more or less simultaneously during the treatment of the film in the reducing solution, the relative rates and proportions of the various reactions, depending, in great part, upon the pH, of the solution. It should first be noted that when using sulphite as a reducer, the pH of the solution must be kept up in the neighborhood of 6.0 in order to insure sufficient sulphite ions being available, as at pH values much below 6.0, the bulk of the sulphite goes into bisulphite, which is not a satisfactory reducing agent for our process. If the pH of the treating solution is kept around 6.0, say between 6.0 and 6.5, the major reaction is probably simple reduction of the ferric ferrocyanide to ferrous ferrocyanide with the consequent loss of approximately of the color when the salt is oxidized back to ferric ferrocyanide by oxidation due to subsequent treating solutions or exposure to the air. As the pH is raised to a value of about 7.0, some of the ferrous ferrocyanide formed by the reduction is converted to ferrous hydroxide or basic ferrous ferrocyanide or both, with a further loss of blue color. These substances are subsequently dissolved out by treatment with acidified water or by the natural acid content of subsequent treating solutions. As the pH is further raised, a greater percentage of the ferrous ferrocyanide is converted to the basic form, so that at a pH of about 8.0, this conversion probably accounts for the major part of the color loss. The OH ions necessary for these reactions may be furnished in any conventional manner, as by the addition of a basic salt such as sodium carbonate, or by the addition of a suitable alkali, such as sodium hydroxide.

When sulphite is used as the reducing agent, there is also a third reaction, to wit: the production of a double or complex salt, formed as the result of some of the ferric ions combining directly with some of the sodium and sulphite ions to form a sodium ferric sulphite complex, which results in a further diminution of color.

As previously mentioned, the conventional blue toning solutions produce an image which also contains a silver salt, and we have found that some of the ferric ions present in the image and fringe combine with some of the silver ions and sulphite ions to produce an insoluble ferric silver sulphite salt. In order for this reaction to go, it is of course necessary that there be silver ions in solution, which may be accomplished by first treating the film with a weak solution of hypo or by adding some hypo to the sulphite bath; or if desired, the film may be passed directly into a hypo bath before the sulphite is washed from the gelatin. If for any reason, there is no sliver salt present in the image at the time it goes into the second treating solution, silver ions may be made available by adding a silver salt such as silver nitrate to the sulphite solution and the reaction will be the same. This reaction goes so long as there is an appreciable quantity of silver and sulphite ions present. When in the claims, we speak of making silver ions available, it is to be understood that we mean to include either dissolving the silver in the film or adding silver to the solution.

The ferrous ferrocyanide formed by the reduction of ferric ferrocyanide is white and insoluble, but is easily oxidized back to ferric ferrocyanide by any one of a number of treating solutions normally employed as subsequent steps in color processing and is also oxidized by mere exposure to the air. However, when it is reoxidized to ferric ferrocyanide, only about /3 as much ferric ferrocyanide is formed as was present originally, so

- that we have a normal diminution of color by reason of this reaction of approximately The ferrous hydroxide and the complex salts (formed when sulphite is used) are acid soluble and may be subsequently dissolved out. Consequently, when in the specification and claims, we speak of removing or eliminating the fringe, it is to be understood that we mean to include both decolorizing a substance and/or removing that substance.

The ferric ferrocyanide which diffuses out from the agglomerated grains of the image is in a colloidal or highly dispersed state, and is therefore more readily attacked by the sulphite ions than are the grains themselves. Hence, the amount of ferric ferrocyanide in the fringe is much less than in the image proper, and the preponderance of sulphite ions in the gelatin of the fringe is so great that they are but little depleted by reaction with the ferric ferrocyanide which means that the reactions go substantially to completion. However, in the image proper, due to the greater concentration of the ferric ferrocyanide therein, it greatly preponderates over the sulphite ions entering that part of the gelatin, and hence the sulphite ions entering the main body of the image are rapidly depleted before a noticeable amount of the ferric ferrocyanide has been converted. Consequently, if the treatment is stopped when the color has disappeared from the fringe, there still will be no appreciable modification of the color or structure of the image proper, although the overall density will be a trifle lighter.

While we have given specific examples of substances and concentrations in describing our invention, it is to be understood that they are merely illustrative of the broad principles thereof as defined in the appended claims.

We claim as our invention:

1. The method of coloring a photographic silver image which includes: treating said image with an iron toning solution comprising a soluble ferricyanide and a soluble ferric salt to produce a diffused Prussian Blue image having a fringe; and then treating said film with a solution containing sodium sulphite, the pH of said solution being above 7, until 'said fringe is substantially eliminated but the color of said image is not materially modified.

2. The method of coloring a photographic silver image which includes: treating said image with an iron toning solution comprising a soluble ferricyanide and a soluble ferric salt to produce a diffused Prussian Blue image having a fringe;

and then treating said film with a solution containing an alkali metal sulphite, the pH of said solution being above 7, until said fringe is substantially eliminated but the color of said image is not materially modified.

3. The method of coloring a photographic silver image which includes: treating said image with an iron toning solution comprising a soluble ferricyanide and a soluble ferric salt to produce a diffused Prussian Blue image having a fringe; and then treating said film with a solution containingnan alkali metal sulphite, the pH of said solution being above 6.5, until said fringe is substantially eliminated but the color of said image is not materially modified.

ALAN- M; GUNDELFINGER. LYNE s. TRIMBLE. 

